That's a 'Low Boy' style fender. Aftermarket. Probably Fiberglass or Composite per edging. If it's metal, then you got something there. Not many in metal. I like them. Old-School-Cool in my book. Thought about one for mine but... I's wanting mines in metal.
yup.... a fiberglass aftermarket fender, no doubt.... lots of folks took off the oem chrome ones. plastics were the most common, but drag specialties did make a steel one (I have one on my 78 and one I got cheap off fleabay)